Port the very basic serial console from mtrr

It's enabled by the flag ENABLE_SERIAL CONSOLE

src/device/serial.c

@@ -51,6 +51,7 @@ enum {
 static int             next_inst = 0;
 static serial_device_t serial_devices[SERIAL_MAX];
 
+//#define ENABLE_SERIAL_CONSOLE 1
 #ifdef ENABLE_SERIAL_LOG
 int serial_do_log = ENABLE_SERIAL_LOG;
 
@@ -193,6 +194,15 @@ serial_transmit(serial_t *dev, uint8_t val)
         write_fifo(dev, val);
     else if (dev->sd->dev_write)
         dev->sd->dev_write(dev, dev->sd->priv, val);
+#ifdef ENABLE_SERIAL_CONSOLE
+    if ((val >= ' ' && val <= '~') || val == '\r' || val == '\n') {
+        fputc(val, stdout);
+        if (val == '\n')
+            fflush(stdout);
+    } else {
+        fprintf(stdout, "[%02X]", val);
+    }
+#endif
 }
 
 static void